1. Field of the Invention
The present invention relates to a liquid cooling unit for electronic systems, which cools electronic elements such as a LSI processor by means of a forced circulation of liquid coolant. More particularly, the invention relates to a liquid cooling unit for electronic devices which improves the cooling efficiency without increasing an amount of the liquid circulation to a cooling plate on which an electronic device is installed.
2. Description of the Related Art
In a typical server system, a plurality of server units are mounted in a rack. The amount of generated heat from LSI processors used in servers has largely increased along with improvements of the processor transmission frequency. There is therefore a shortage of cooling capacity for the conventional forced air cooling in a spatially limited server enclosure, while the liquid cooling has a potential advantage of higher cooling capability.
FIG. 1 is a descriptive view of a conventional liquid cooling system used for electronics cooling. In FIG. 1, the circulation loop is formed so that the liquid coolant is pressure-supplied by the pump 102, and after flowing through the cooling plate 104 which cools electronic elements, heat of the coolant is dissipated by the heat exchanger 106 and the coolant is returned to the reservoir tank 100.
More specifically, the liquid coolant is pressure-supplied by the pump 102 to the cooling plate 104. An electronic element such as a LSI processor is mounted on the cooling plate 104, and is cooled indirectly by forced circulation of the liquid coolant. The high-temperature coolant leaving the cooling plate 104 enters the air-cooled heat exchanger 106, and after being cooled to a temperature near the ambient temperature by outside air convection, the coolant is returned to the reservoir tank 100, and these steps are repeated.
For achieving a higher cooling ability of a liquid cooling system, it is an usual practice to connect two pumps 102-1 and 102-2 in parallel as shown in FIG. 2A, or connect the pumps 102-1 and 102-2 in series as shown in FIG. 2B, thereby increasing the flow rate of the liquid coolant passing through the cooling plate 104.
FIG. 3 is a descriptive view in which the conventional liquid cooling system as shown in FIG. 1 is incorporated into a server enclosure. In FIG. 3, a system board 112 is provided in the server enclosure 110, and LSI processors 114-1 and 114-2 and memory cards as well as other components 116 are packaged on the system board 112. The cooling plates 104-1 and 104-2 are mounted on the processors 114-1 and 114-2, respectively.
The server enclosure also incorporates hard disk drives 120-1 and 120-2, a CD-ROM driver 122, a power supply unit 124, a blower fan 126, and air fans 128-1 to 128-4.
A liquid cooling unit 130 is arranged adjacent the system board 110, has a coolant reservoir tank 100, a pump 102, a heat exchanger 106, and a blower fan 132. The liquid cooling unit 130 includes piping from the pump 102 to the cooling plates 104-1 and 104-2 that mounted on the processors 114-1 and 114-2, the liquid coolant returns to the heat exchanger 106, then thus to the reservoir tank 100.
In such a conventional liquid cooling system for electronic devices, however, there is a demand for high-performance and compact in order to achieve a high density packaging of electronic devices such as a server, particularly achievement of a thinner enclosure. The cooling performance largely depends upon a heat dissipation capability of the heat exchanger, reducing the size of the heat exchanger may have a problem resulting in a decreasing of cooling ability.
The cooling plate mounted on the electronic device, in which the coolant flows through thin or narrow channels will suffer from a large pressure loss. Thus, a flowrate of the liquid coolant through the heat exchanger is considerably reduced, limiting the cooling ability seriously.